Wellbores are drilled in geological formations (on land or offshore) to locate and recover hydrocarbons. A downhole drilling tool with a bit at an end thereof is advanced into the ground to form the wellbore. As the drilling tool is advanced, a drilling mud is pumped through the drilling tool and out the drill bit to cool the drilling tool and carry away cuttings. The fluid exits the drill bit and flows back up to the surface for recirculation through the tool. The drilling mud is also used to form a mudcake to line the wellbore.
During the drilling operation, it is desirable to perform various evaluations of the formations penetrated by the wellbore. In some cases, the drilling tool may be provided with devices to test and/or sample the surrounding formation. In some cases, the drilling tool may be removed and a wireline tool may be deployed into the wellbore to test and/or sample the formation. These samples or tests may be used, for example, to locate and evaluate valuable hydrocarbons.
Formation evaluation often involves drawing fluid from the formation into the downhole tool for testing and/or sampling. Various devices, such as probes, are extended from the downhole tool to establish fluid communication with the formation surrounding the wellbore and draw fluid into the downhole tool. A probe is an element that may be extended from the downhole tool and positioned against the sidewall of the wellbore. A packer at the end of the probe is used to create a seal with the wall of the formation. The mudcake lining the wellbore is often useful in assisting the packer in making the seal. Once the seal is made, fluid from the formation is drawn into the downhole tool through an inlet in the probe by lowering the pressure in the downhole tool.